The development and integrity of blood vessels are regulated by cascade of signaling events triggered by both intrinsic and extrinsic cues. The long term goal of these studies is to determine the identity and function of the genes that are involved in the process of vascular development and to examine how aberrant functions can lead to vascular disorders. For angiogenesis to occur, resting endothelial cells (ECs) need to be activated to emerge out of their relative state of quiescence and to initiate signaling cascade that will lead to proliferation, ECM degradation and cell migration. A growing number of growth factors and cytokines such as bFGF, VEGF and TNF-alpha promote angiogenesis. Although, different angiogenic factors stimulate initially distinct signaling pathways they activate common downstream events such as activation of MAP kinases leading to transcriptional activation of several gene products necessary for new blood vessel formation. Cell surface molecules such as integrins and CAMs have been shown to be involved in this process however, there has been conflicting data regarding the essential role of integrins in angiogenesis. We have recently shown that Junctional Adhesion Molecule-A, JAM-A, a member of Ig superfamily is a key regulator of angiogenesis induced by bFGF. However, the mechanism by which JAM-A regulates this product is not elucidated. The proposal seeks to investigate the mechanism of regulation of angiogenesis by JAM-A and the contribution of the other JAM family members in this process in the following three specific aims. 1) Mechanism of regulation of growth factor-induced angiogenesis by JAM-A will be investigated in vitro by using ECs and in vivo using JAM-A null mice. 2) Intracellular signaling pathway induced through JAM-A will be studied by identifying signaling proteins that may associate with JAM-A and by dissecting the downstream signaling events using specific inhibitors. 3) Cross talk between JAM family members, JAM-A, JAM-B and JAM-C will be investigated both in vitro and in vivo using knockout animals. This investigation has the potential to increase our understanding of vascular disorders that lead to cardiovascular diseases and stroke. Further, elucidation of the role of JAM-A in endothelial cell proliferation and migration leading to angiogenesis will open up a mew line of investigation that is important in tumerigenesis and vascular biology.